A known technique manufactures a solid polymer fuel cell separator by shaping metal material such as stainless steel (refer to Patent Document 1). When a separator is made of material such as stainless steel, an oxide film (passive film) exists on the surface of the substrate. The oxide film has greater contact resistance than a base material of stainless steel to generate joule heat in a contact portion between the surface of the substrate and an electrode. This may result in great loss of heat, thereby reducing efficiency of power generation by the fuel cell.
Patent Document 1 discloses a separator having a substrate made of stainless steel, of which the surface is acid-cleaned to remove an oxide film from the substrate. Furthermore, a coating containing particle mixture of graphite particles and carbon black is formed on the surface of the substrate. Patent Document 1 discloses that removal of an oxide film reduces contact resistance when such a separator is in use.